Enhancement of the thermopower in in the large-x regime ()

✍ Scribed by Minhyea Lee; Liliana Viciu; Lu Li; Yayu Wang; M.L. Foo; S. Watauchi; R.A. Pascal Jr.; R.J. Cava; N.P. Ong

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 519 KB
• Volume: 403
• Category: Article
• ISSN: 0921-4526
• DOI: 10.1016/j.physb.2007.10.320

✦ Synopsis

We observe two distinct phases of Na x CoO 2 in the large Na-doping region (xX0:75), a pure phase H 2 , and a mixed phase

The H 2 phase is characterized by a steep increase of the Peltier conductivity a defined as J ¼ aðÀrTÞ, where J the thermoelectric current driven by the temperature gradient ÀrT. The mixed-phase state H 2 þ H 3 exhibits an unusual layered phase separation with conducting layers existing in parallel with insulating ones. At the critical doping x p $0:85, the figure-of-merit Z at 80 K is 40 times larger than that of the as-grown sample (x$0:7). The Hall coefficient and magnetoresistance are also reported.